Modulated infrared sources are employed to countermeasure heat seeking missiles which home in on the heat generating portions of a target such as the engines of an airplane. These modulated infrared sources must produce a signal of sufficiently high intensity compared to that generated by the target.
Certain of such modulated infrared sources include a single large source for producing ample amounts of infrared energy and at least two modulating elements, at least one of which is rotating, to intercept the output from the source so as to provide modulation thereof. These modulating elements are discs comprising alternating transparent and opaque radial segments. One of the modulating elements (the stator) is disposed with respect to the source to block a predetermined amount of the radiation from the source at all times and the other alternately blocks and passes the remaining radiation passing the first modulating element. This type of modulated infrared source is, relatively inefficient since even at the modulation peaks substantially one half of the available energy from the source is rejected (blocked).
Accordingly, it is an object of this invention to provide improved means for modulating the output from an infrared radiation source.
It is another object of this invention to provide a more efficient means for modulating the output from an infrared source.
Briefly, in one embodiment apparatus for more efficiently modulating an infrared radiation source comprises a collecting member for collecting and collimating the output from an infrared radiation source and applying it to the stator assembly of a modulator. The stator assembly includes a disc of alternating opaque and transparent radial segments having a plurality of optical wedges disposed on the opaque segments of the disc and further having a reflecting and collimating needle disposed in the center of the disc. The needle reflects source energy which normally would be absorbed by obscuration and the optical wedges re-image the source through discrete apertures rather than reflecting energy back to the source. This energy is directed to a first rotating element. The rotor comprises a disc having alternating transparent and opaque radial segments to alternately pass or block the radiation received from the stator. A further modulation can be imposed on the output from the aforementioned rotor assembly by a second rotor assembly which is preferably constructed in very much the same fashion as the stator.